Control of Internal Corrosion of Petroleum Products Pipelines With Oil Soluble Inhibitors★

Abstract

Abstract This article summarizes the corrosion inhibitor program of a products pipeline system since its initial operation eight years ago. Initially alkaline sodium nitrite solutions were utilized for corrosion protection. This material was an effective corrosion inhibitor, but its use resulted in the production of large quantities of rust and scale, and in addition contributed to water cloud problems. Use of an oil soluble corrosion inhibitor minimized these problems and resulted in improved protection of the pipeline. During the past three years an average internal corrosion rate of only 0.025 mil per year was observed, in spite of the fact that prolonged periods occurred when no inhibited product contacted sections of the pipe. A mechanism explaining the behavior of oil soluble corrosion inhibitors in a pipeline is presented. This theory accounts for the outstanding effectiveness of such materials and explains why they protect the metal during the prolonged periods when uninhibited stocks are present. The use of more than one oil soluble corrosion inhibitor in products transported through a pipeline causes mixtures of inhibitor molecules to be adsorbed on the surface of the pipe. One inhibitor in contact with the pipe tends to displace another inhibitor previously adsorbed on the surface. This results in some interchange of the corrosion inhibitors in the products transported. The degree of protection realized from the use of several corrosion inhibitors in a pipeline system is discussed. 5.8.2